Carbamate Insecticides Dr Kumari Anjana Assistant Professor Deptt
Carbamate Insecticides Dr. Kumari Anjana Assistant Professor Deptt. of Veterinary Pharmacology & Toxicology Bihar Veterinary College, Bihar Animal Sciences University, Patna
Content of the chapter • • Introduction Classification Similarities with organophosphate compounds Differences from OP compounds Mechanism of action Clinical signs Diagnosis Treatment
Carbamate Insecticides • The carbamate insecticides represent the third major group of synthetic organic insecticides developed after World War II. • Carbamate Insecticides are widely used in agricultural, veterinary and household practices by virtue of their properties like; ü broad-spectrum of activity, ü low mammalian toxicity and ü rapid environmental inactivation.
Classification • Naphthyl carbamates- Carbaryl (sevin). • Phenyl carbamates – Propoxur. • Heterocyclic methyl carbamatespyrolan and isolan. • Heterocyclic dimethyl carbamates. Carbofuran and furadan. • Oximes- aldicarb, methomyl and thiodicarb.
Similarities with organophosphate compounds • Carbamate insecticides are similar to organophosphorus insecticides in most of their properties like: – mode of action, – range of toxicity, – lack of environmental persistence and – lack of safety for beneficial insects and non- target species. – Similar to OP compounds, they do not have cumulative properties.
Differences from OP compounds Carbamates differ from OP compounds in following aspects: --They are reversible inhibitors of cholinesterase (Ch. E) enzyme. – They inhibit cholinesterase at both anionic and esteratic sites. – They are selective inhibitors of cholinesterase enzyme and do not inhibit carboxylesterase enzyme. – Decarbamoylation (reactivation) of inhibited Ch. E enzyme is easier. – Cholinesterase enzyme reactivators like 2 -PAM are ineffective (contraindicated) in the carbamate intoxication.
Mechanism of action • Carbamate inhibit acetylcholinesterase enzyme, but these insecticides occupy both anionic and esteratic sites of ACh. E. • The inhibition in case of Carbamate results from a chemical reaction between the carbamoyl moiety of carbamate compound and the active site serine hydroxyl group of ACh. E to form carbamoylated enzyme rather than phosphorylated as with the organophosphate. • The carbamoylated enzyme is relatively less stable and susceptible to hydrolysis, although rate of hydrolysis is not very fast as with acetylcholine.
• Therefore, the decarbamoylation is easier in comparison to dephosporylation (OPs). • Because of relatively rapid reactivation of carbamoylated ACh. E, the carbamate insecticides are often called reversible anticholinesterase agents. • Toxicosis develops when the amount of carbamate pesticide in the body is so large that the rate of carbamoylation of ACh. E exceeds the rate of hydrolysis of pesticide by the enzyme.
Clinical signs Muscarinic signs: Profuse salivation (watery drooling), bronchial secretions and constriction, diarrhoea, frequent urination and miosis. Nicotinic signs: Muscular tremors, convulsions, paralysis of respiratory muscles and dyspnoea. CNS signs: Restlessness, ataxia, depression of respiratory and vasomotor centres, paralysis, coma and death due to respiration failure followed by cardiovascular failure.
Diagnosis: • History, circumstantial evidence, • Clinical signs, • Estimation of blood Ch. E activity (25% or more decrease in OPI and carbamate toxicity) and • Identification of the insecticide in feed, water, ruminal content or tissues. Treatment: • Atropine sulphate only • Not Ch. E-reactivators.
Members • Carbaryl: used as ectoparasiticide in animals. • Carbofuran: It is extensively used as a soil insecticide, where it has replaced cyclodienes for control of seed eating pests of grain crops.
Propoxur: • It is used to control house-hold insects such as cockroaches, bedbugs and wasps. • It is also used as a replacement of DDT for malaria control and is applied against a number of food, vegetable and ornamental pests. Methomyl: • It is a broad-spectrum oxime carbamate which is highly effective against many plant feeding insects and also has high ovicidal activity.
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